Bake Texture to New UVMap (2.92)
You've chosen to bake with the Emit option, it will bake what's emitted, but your object doesn't use any Emission node. In the linked page, the Image Texture is plugged into a Viewer node, which acts like an Emission node. If you want to bake the Diffuse, choose Diffuse instead, and under Influence only enable Color.